Method of pressing blanks of molded pulp



Sept. 23, 1952 E. M. CHEVRIER 2,611,154

METHOD OF PRESSING BLANKS OF MOLDED PULP Filed Sept. 15. 1949 I I 1 l it? i. m. am

2 i! m wwz Patented Sept. 23, 1952 METHOD OF PRESSING BLAN KS OF MOLDED PULP Eugene Marcel Chevrier, Montrougc, France Application September 13, 1949, Serial No. 115,539 In France September 17, 1948 3 Claims. 1

. In the manufacture of objects constituted by paper pulp or the like there are first made shaping forms, of a shape which is to that of the object fabricated. The pulp blanks exhibit a lumpy surface, and their material is present in the form of an entanglement of practically dry fibers constituting a speciesof felt whose-density and compactness are very small. Moreover, the

production of the blank requires a finishing operation termed calendering, whose purpose consists in imparting to the object the requisite qualities of surface smoothness and compactness.

Since the material of the blank, owing to its dry and fibrous texture, is unable to undergo relative sliding of the parallel layers which con-j s'titute it without rupture of fibers, to cause .tears in the blank, this calendering can only consist of a squeezing or flattening of the material of the blank. In the fabricating practice this has, been accomplished, until now, by subjecting the blank to a powerful compression in molds corresponding to the final form of the object. But this procedure, if it is to be effective, requires the application of considerable pressures, reaching theorder of 600 kg. per sq. cm., which require the employment of equipment which is costly, cumbersome and usually complicated.

The present invention relates to a method of surface pressing blanks of the type described, to equipment adapted for use in operating said method, and it is further directed to the application of such method and equi ment to the manufacture of moulded paper articles, whereby the above-mentioned drawbacks are eliminated. The

invention essentially consists of subjecting the "walls of the blank to a sort of extrusion or shearing effect between a part fixed with respect to the blank and a part moveable with respect thereto, somewhat similar in effect to the action sustained by a'cloth being ironed, and such operation preferably being carried out in hot condition. More specifically, where the blanks tobe pressed are of a generally cylindrical form, whether circular in cross-section or otherwise, the above- 'described operation is carried out by first mounting the blank over a suitable cylindrical'ma'ndrel and then forcing it through a sleeve. This sleeve comprises a tapered or similar portion for thermosettable substance, since this will result in a more satisfactory conformation of the blank anda welding of the fibres which is effective to improve the homogeneity and compactness of the product. The temperature should be determined in relation to the flow point of the material used.

The relative slipping movement of the blank with respect to the die or equivalent member used is facilitated by spraying thereon a suitable lubricant such as a water solution of soap.

In the manufacture of boxes and similar articles, the bottom wall of the box may be pressed by direct compression thereof after the cylindrical part of the box has been subjected to the above-described shearing or extruding process.

The method of the invention makes it possible to produce ribs or beads in the bottom walls of boxes or the like. For this purpose, there is formed in the end wall of the mould (the sides of which are formed by the die) an annular recess complementary in shape to the desired bead, and the bead in the box is produced by squeezing into said recess the excess blank material formed during the pressing of the side walls of the box, by means of a moveable ring interposed between the die and the bottom wall.

The production of finished articles from blanks may thus be accomplished with the use of comparatively low pressures, this in turn involving the use of simple and inexpensive equipment. Moreover, while heretofore it was necessary,

when manufacturing the blanks, to start from high grade refined pulp stock, in employing the method of the invention it is' possible to start from cruder grades of pulp, so remarkableis the degree of improvement in the quality of the product as resulting from the above-described pressing-process. Finally, the great simplicity of the operations comprising the method of the invention makes it possible to attain in production output rates which it was impossible to .attain heretofore.

The accompanying drawings illustrate by way of example and to facilitate intelligence of the invention some embodiments thereof.

Figure 1 is a diagrammatical axial section illustrating the pressing of the cylindrical portion of a blank.

Figures 2 and 3 diagrammatically illustrate in axial section the manner in which a bottom bead may be obtained. Y

Figure 4 is a section through a blank of a box cover or lid.

Figure is a diagrammatical axial section illustrating the manner in which a finished lid may be obtained by pressing according to the procedure of the invention.

Figures 6 and 7 are diagrammatical axial sections, on a small and an enlarged scale respectively, showing how a restriction of slightly reduced diameter may be obtained throughsurface pressing bythe method of the invention.

As shown in the drawings, and more particularly figure 1, according to the present invention, the surface pressing operation may be accomplished by mounting the blank I over a mandrel 2 and forcing the mounted assembly bodily through a sleeve 3 performing the function of a die. The mandrel 2 is cylindrical and the die 3 comprises a cylindrical portion 6 and a tapered or similar entrance portion 5, these'portions being preferably separated by a clear-cut edge 4. I It has been found that optimum results may be obtained where the half cone angle ofthe taper is about 28 to 30. Considering th comparative brittleness of blanks made of moulded pulp, it could at first glance be feared that breaks or cracks might occur in the blank as a result of such an operation, especially at the point where the blank is first gripped between the die and the mandrel. .I have found however by experience that from the very instant the wall of the blank is engaged between the mandrel 2 and .the die 3 the blank is drawn on by the mandrel without any relative slippage occurring between it and the mandrel, while it flattens out in sliding over thetapered surface 5 and the sharp edge 4 of the sleeve or die 3, thus acquiring the desired surface smoothness and compactness. To facilitate this operation, it is desirable to'spray a suitable lubricant, for instance an aqueous soap solution, over the blank inthe area at which it penetrates the die.

.Preferably, the operation is carried out in hot condition. It is desirable when preparing the blanks to add to the fibre a thermoplastic or thermosettable substance in a variable amount which may reach as high as and even somewhat higher. A suitable temperature for the application of the method of the invention with blanks of such type containing thermoplastic substances is in a range of from 100 C. to 140 C., and preferably about 120 C.

Where a box'is to be formed by my improved method, the bottom wall may be simply pressed by direct pressure, as in usual procedure, subsequently to the above-described operation; and

such bottom forming step may be efifected at the I end of the above-described pressing stroke, the bottom of the blank being squeezed or pressed against a metal backing plate- (not shown) placed above the die 3.

The method is especially convenient, in manufacturing boxes and similar articles, for forming a rib or bead around the edge of the bottom of the box. For such purpose, the following procedure may be followed. The blank is placed upon the mandrel in such a manner that there 'remains above the mandrel a sufficiently large portion of the blank to form, by pressure against the bottom 1 (see Fig. 2), an annular bead .8 which will fill a groove 9 formed in said bottom.

Above the die 3 an annular sleeve I0 is arranged which remains in contact with the die throughout a first part of the stroke of the mandrel 2 and also preferably until the time the mandrel will have engaged against the bottom I. The

annular sleeve then separates from the die 3 and assumes the position shown at 10' in Fig. 3, thus 4 imparting through pressure the final desired form to the bead or rib trapped within the groove 9.

Where it is desired to produce a box capable of being accurately sealed with a lid, by the method of the invention, the following procedure may be used:

A lid blank is formed, such as shown in Fig. 4,

, comprising a down turnedflange I I. This blank is passed over a mandrel comprising an external cylindrical part l4 and an inner body IS. The assembly is then bodily inserted into the dual sleeve l6, I! which comprises a tapered or similar entrance surface l2 playing a similar part as the corresponding part 5 of Fig. 1. The lid will thus be formed in a manner to fit over the top edge of a box which will accurately assume the position occupied by part I 4 of the mandrel in Fig. 5.

'To secure improved sealing engagement of the .box, it may be preferable still further to improve the accuracy with which the edges are formed that are adapted to receive thereon the lid manufactured as described above, and. for this purpose,

' form a part with a diameter smaller than that of the body of the box, by an amount corresponding to the thickness of the lid. For this purpose, after completing the operations described with reference to Figs.; 1, 2 and 3, there may be performed a further surface-pressing step on the cylindrical part-of the box, this operation. only involving a verticalextent of the box corresponding in length to that of the outer cylindrical part II of the lid. This step may be carried out, as shown in Figs. 6 and '7, by using a mandrel and a. die in which the active surfaces [8 and I3 correspond in diameter to the dimensionsof, the restricted portion of, the final box. .-Ihe. mandrel 20 having the box 2| passed over itis inserted into the die 22 in thesame wayas above-described in connection with Fig. 1 this time, however, the lip portionsof the. box .are. directed toward the die. Upon engaging the entrance surface, 23 .of the die, the lip 24 of the box is deflected until it bears against the mandrel 26 (Fig.7) -However, after the time said lip has passed beyond the edge 21 of the die and is gripped between the dieand the mandrel, the box is drawn along by the mandrel without the body of the box-being subjected to any undue crushing strain, and the restriction 25 is produced as shown in broken lines in Fig. 7. The above examples referring-mainly to the manufacture of boxes are' in no way restrictive. The invention makes it possible to form articles of all kinds of' cylindrical shape, from blanks having a contour approximating that of the final article. The invention is, moreover independent from the particular manner in which suchblanks may have been produced:

The invention isfurthermore intended to 'cover in its scope of protection the new articles of manufacture producedthrough' theuse of the method described.

I claim: I .1. A process for manufacturing molded paper articles having substantially cylindrical lateral walls, comprising, forming a cylindrical paper blank, said blankhaving approximately the final form of the molded article,.mounting said blank upon a cylindrical-mandrel whose cross-section is equal to the interiorcross-section of the molded article, and forcing said blank mounted upon said mandrel through a-die having: aicylindrical portion whose cross-sectionis .equalto the exterior cross-section of said article and which has a flared entrance whose inclination is substantially 28.to 30 relativeto the axis, said entrance surface of said die being connected with the cylindrical portion thereof by a clear cut edge.

2. A process as set forth in claim 1 wherein the material forming the blank contains in addition to the paper a thermoplastic substance.

3. A process as set forth in claim 1 wherein the material forming the blank contains in addition to the paper a thermosetting substance.

EUGENE MARCEL CHEVRIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 209,686 House Nov. 5, 1878 924,555 Jenkins June 8, 1909 Number 11 Number Name Date McCulloch Sept. 26, 1933 Kobberup et al Aug. 24; 1937 White Oct. 29,1940 Millspaugh July 22,1941 Wiley Dec. 28', 1943 Stahl Feb. 29,1944 Wiley May 16,1944 Slater Apr, 10, 1945 Wisman Aug. 12,1947 Palmer et a1 Aug. 12,1947 Messinger Oct. 18,1949

FOREIGN PATENTS Country Date Switzerland Jan. 16, 1939 Great Britain Sept. 20,1940 

